Preventing Ammonia Gas Accidents
Ammonia (NH3) is a colorless gas that both occurs naturally in the environment and is also man-made for industrial purposes. In nature, bacteria, decaying plants and animals, and animal waste in the soil produce the gas. Ammonia is manufactured by mixing natural gas with steam, which is reformed over a catalyst bed to produce hydrogen and carbon dioxide. The hydrogen and nitrogen, from the air, react in a final catalyst bed to produce ammonia gas, which is cooled for tank storage.
Anhydrous ammonia is most commonly used in fertilizer for agriculture, which accounts for 80 percent of its use in the U.S. Other primary applications are refrigeration, food/beverage processing and the electric power industry. Secondary applications include:
Safe Exposure Levels
The Occupational Safety & Health Administration (OSHA) has set a limit of 25 parts-per-million (ppm) in the workplace during an 8-hour shift and a short-term limit (15 minutes) of 35 ppm. International standards for ammonia exposure are similar to those in the U.S. The effects of ammonia exposure range from irritating smells to life-threatening situations.
The Environmental Protection Agency (EPA) regulates ammonia under the Clean Air Actís General Duty Clause [Section 112(r)(I)] and Risk Management Program (RMP) Rule [40 CFR 68]. Facilities with over 10,000 pounds of ammonia are required to develop a hazard assessment, a prevention program, an emergency response program and submit a risk management plan to the EPA.
Anhydrous ammonia is liquefied under pressure when stored in tanks. If released to ambient air accidentally, it expands up to 850 times. It may also aerosolize and behave like a dense gas even though it is usually lighter than air. Water vapor also may condense in the air to create a white cloud. Rather than dispersing, the cloud can travel along the ground and pose exposure hazards for workers and the public.
The U.S. Department of Transportation requires that anhydrous ammonia storage tank containers meet specific requirements. For example, some ammonia tanks must have rated pressure relief devices to reduce the possibility of over pressurization and explosion. Non-corroding valves and hoses are also required for safety on tanks.
Reliable ammonia detection ensures both personnel safety and product quality. The nose may detect concentrations as low as 5 ppm. Typical exposure symptoms are irritation of the eyes, throat and respiratory organs. At a few hundred ppm, irritation of the mucous membrane of the eyes occurs. Breathing is intolerable at about 1000 ppm and vision may be impaired. The risk of fatality rapidly increases at concentrations of around 2500 ppm.
In addition to personal injury, ammonia accidents can result in considerable equipment, materials, product and property losses. According to the EPA and Factory Mutual, ammonia releases have resulted in several catastrophic losses ranging up to several million dollars. Such losses have resulted from ammonia contamination to product, as well as explosions because ammonia is potentially combustible.
Application - Fertilizer & Agriculture
Ammonia as fertilizer for agricultural applications is a valuable source of nitrogen, which is essential for plant growth. Depending upon the particular crop being grown, up to 200 pounds of liquefied gas (anhydrous ammonia) per acre may be applied to the soil during the growing season. The liquefied ammonia is kept in pressurized tanks, which are tractored out to the field for direct application to the soil.
In producing ammonia fertilizer (anhydrous ammonia, ammonia hydroxide and similar products), the gas is converted into a liquid form and pressurized. In the liquefaction process, hazards such as gas leaks at fittings, valves and pipe transfer joints can occur. On-line ammonia gas detection should be available at critical stages in the production process. Above-ground ammonia storage tanks also should be brought into the detection and monitoring loop by manufacturers and distributors.
Ammonia Gas Monitoring
General Monitors' TS4000H Toxic Gas Detector and MC600 Multi-Channel Controller offer an ideal ammonia gas monitoring system. A single MC600 controller can be hardwired to up to six TS4000H detectors installed at strategic locations in a facility. This system provides high-performance, low-cost-per-point ammonia detection.
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